Apparatus and method for two-component bioelectrical impedance ratio measuring and monitoring

Abstract

An implantable cardiac stimulation and rhythm management device includes an impedance measuring circuit which determines a patient's intra-thoracic impedance and the resistance and reactance components of the impedance. The device includes a microcontroller which calculates a ratio (Z/R) which equals the reactance (Z) divided by the resistance (R). The microcontroller is configured to use the calculated ratios to establish a baseline intra-thoracic fluid level, an upper bound relative to the baseline, and a lower bound relative to the baseline, and to monitor the Z/R ratio relative to the baseline and upper and lower bounds. When the Z/R ratios are outside of the established bounds, operating parameters of the stimulation and rhythm management may be altered by the microcontroller.

1. An implantable cardiac stimulation and rhythm management device for measuring intra-thoracic fluid impedance comprising:
 at least one impedance measuring electrode; 
 an impedance measuring circuit coupled to, and in communication with, the at least one impedance measuring electrode, wherein the at least one measuring electrode is operative to measure resistive (R) and reactive (Z) components of impedance; 
 a microcontroller connected to the impedance measuring circuit and configured to calculate ratios (Z/R) that equal the reactive components divided by the resistive components Z/R values has; and 
 a memory connected to the microcontroller and the impedance measuring circuit and operative to store the measured reactive (Z) and resistive (R) components and the ratios; 
 wherein the microcontroller is further configured to directly monitor the calculated ratios over a period of time to establish a baseline intra-thoracic fluid level for the patient and an upper bound relative to the baseline and a lower bound relative to the baseline, wherein the upper bound and the lower bound account for normal variations in intra-thoracic fluid levels over time for the patient, and to continue to directly monitor the calculated ratios relative to the baseline, upper bound and lower bound. 
 
   
   
     2. The implantable cardiac stimulation and rhythm management device of  claim 1 , wherein the memory is further operative to store programmable operating parameters related to cardiac stimulation used by the microcontroller. 
   
   
     3. The implantable cardiac stimulation and rhythm management device of  claim 2 , further comprising an external device connected to the microcontroller and operative to receive the measured reactive (Z) and resistive (R) components and the calculated ratios. 
   
   
     4. The implantable cardiac stimulation and rhythm management device of  claim 3 , wherein the external device is further operative to modify the cardiac stimulation operating parameters stored in the memory based on the measured reactive (Z) and resistive (R) components and the calculated ratios. 
   
   
     5. The implantable cardiac stimulation and rhythm management device of  claim 4 , further comprising a telemetry circuit in communication with the external device and the microcontroller. 
   
   
     6. The implantable cardiac stimulation and rhythm management device of  claim 1 , wherein the at least one impedance measuring electrode comprises at least one of the group consisting of ventricular tip electrode, ventricular ring electrode, right ventricular coil electrode, and superior vena cava electrode. 
   
   
     7. The implantable cardiac stimulation and rhythm management device of  claim 1 , wherein the microcontroller is operative to determine if one of the ratios is located inside or outside the established upper bound and lower bound. 
   
   
     8. The implantable cardiac stimulation and rhythm management device of  claim 7 , wherein the memory is further operative to store programmable operating parameters related to cardiac stimulation used by the microcontroller and the microcontroller is operative to automatically modifying at least one of the cardiac stimulation operating parameters in response to the location of the ratios. 
   
   
     9. The implantable cardiac stimulation and rhythm management device of  claim 2 , wherein the microcontroller is further operative to modify the cardiac stimulation operating parameters stored in the memory based on the measured reactive (Z) and resistive (R) components and calculated ratios.